"A shooter" and for braggin' rights are two different things. To me for bragging rights it is a 5 shot group at 100yds. I have shot many groups of 3 shots just to do preliminary load work-up. If the group shows potential it is recorded for further expiermentation.
A real "tell" for me is how did the shot feel. For me,keeping my head down (follow through) and anticipating recoil are my groups biggest killers. I have shot plenty of 5 shot groups that 3 or 4 shots are into <.250" then the others open the group to MOA or bigger. Some . . . MUCH bigger. That is usually me.
IMO,if a shooter puts three in a tight group,that is neither coincidence OR luck. He did something extremely RIGHT for those shots.
However that is arguable/debateable. Five shots in a tight group or evenly spaced out,a half inch apart to bring the group to 3 or 4 inches at 100 . . OR . . <.500" at 100 is either something very wrong with gun,optics,and/or shooter . . OR . . something very right with same.
A shooters "follow through" is a problem that alot of shooters have, and they or their shooting buddy, that should be watching them,is not even awhare that they have.
After the shot breaks I keep the tight cheek weld and looking through the scope/sight for 2 seconds. This is something that you have got to train for. It is not natural.
Give it a try. IT WILL improve your groups. --- SAWMAN